High power hydraulic cylinder

ABSTRACT

A hydraulic device that includes a case, and a substantially hollow rod slidably extending from the case. The rod has a ram on a first end thereof that caps the rod to form a first hydraulic piston. The rod has a second hydraulic piston on a second end thereof, inside the case. The first and second pistons are at least partially radially coextensive, and a pressure barrier inhibits high pressure on the first piston inside the hollow rod from reaching a side of the second piston that faces the first piston.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of U.S. Provisional Patent Application No. 61/426,420 entitled “LIGHTWEIGHT CYLINDER,” filed Dec. 22, 2010, the contents of which are hereby incorporated by reference.

FIELD OF INVENTION

This disclosure relates to hydraulic systems in general and, more particularly, to hydraulic actuators.

BACKGROUND

Hydraulic systems are ubiquitous in the modern age. Nearly every machine in which a linear actuation or force is needed or can be used to produce a desired end can be constructed with hydraulics. Hydraulic systems are often more reliable, powerful, and versatile that electric based actuators. Additionally, hydraulic pumps can easily be driven from power take off (PTO) devices that are commonly built into industrial transmissions.

Although hydraulic systems provide a good power to weight ratio, and are ultimately may be powered by the same engine that moves a vehicle, they are limited by the available pressure and the overall physical dimensions of the actuators and pistons. In order to make a more powerful hydraulic actuator, one has to increase the pressure to the actuator, or increase the size of the actuator. Naturally, application of pressure has an upper limit as pumps, seals, and gaskets can only operate within a limited range of specifications before part failure is imminent. The technique of increasing the size of the actuator also has limits as this increases the overall size and bulkiness of the completed system.

What is needed is a device and method that addresses the above, and related, issues.

SUMMARY

The invention of the present disclosure as disclosed and claimed herein, according to one aspect thereof, comprises a hydraulic device that includes a case, and a substantially hollow rod slidably extending from the case. The rod has a ram on a first end thereof that caps the rod to form a first hydraulic piston. The rod has a second hydraulic piston on a second end thereof, inside the case. The first and second pistons are at least partially radially coextensive, and a pressure barrier inhibits high pressure on the first piston inside the hollow rod from reaching a side of the second piston that faces the first piston.

In one embodiment, the hydraulic device includes a rod guide inside the case and coaxial thereto, with the second piston slidably interposing the case and the rod guide. The pressure barrier may interpose the guide rod and the substantially hollow rod. A high-pressure, variable volume in the device may comprise a first volume inside the guide rod, a volume bound by the case and the second piston, and a volume between the first piston and the pressure barrier. In some embodiments, a low-pressure, variable volume inside the device comprises an area bound by the case, the guide rod, the second piston, and the pressure barrier.

The case and ram may be urged apart by a relatively high pressure fluid inside the high pressure volume compared to the low pressure volume, and the case and ram may be urged together by a relatively high pressure fluid inside the low pressure volume relative to the high pressure volume. A high-pressure port may be provided on the case entering the high pressure volume, and a low pressure port may be provided on the case entering the low pressure volume. Some embodiments include at least one pressure equalizing port defined in the rod guide; some include at least one pressure equalizing port defined in the hollow rod.

In some embodiments, the case and rod guide have a substantially circular cross-section. The rod guide may attach inside the case on a first end thereof, and may have a second tapered and threaded end that accepts the pressure barrier and retains the pressure barrier against the tapered end by an attached threaded cap. The device may also include a retainer on an open end of the case engaging the hollow rod and preventing the second cylinder from contacting the pressure barrier.

The invention of the present disclosure, in another aspect thereof, comprises a device having a substantially cylindrical case with a first, open end and a substantially cylindrical guide member inside thereof attached to a second end, the case and guide member being substantially coaxial. The device includes a fixed pressure barrier on an end of the guide member proximate the open end of the case. A first piston defines a hollow center and is located between the case and guide member, the piston being movable between the pressure barrier and the second end of the case. A hollow rod attaches on a first end to the first piston, encircles the pressure barrier, and attaches on a second end to a second piston.

In some embodiments, the guide member defines a pressure equalizing port proximate the second end of the case such that a first single pressure volume of variable total size is defined by 1) the variable volume bound between the first piston, the case, and the guide member, 2) the volume inside the guide member, and 3) the volume between the pressure barrier, the second piston, and the hollow rod. A hydraulic port may be provided on the case accessing the first single pressure volume.

The guide member may have a tapered portion and a threaded end, the guide member retaining the pressure barrier between the tapered portion and the threaded end by an attached threaded cap. Some embodiments will have a retainer attached to the open end of the case and abutting the hollow rod on a side opposite the pressure barrier such that the hollow rod slides into the retainer, the retainer sealing the second end of the case to prevent the first piston from leaving the case

In some embodiments, the hollow rod defines a pressure equalizing port proximate the first piston such that a second single pressure volume of variable total size is defined by 1) the variable volume bound inside the hollow rod, outside the guide member, and between the first piston and pressure barrier, and 2) the variable volume bound outside the hollow rod, inside the case, and between the first piston and retainer. A hydraulic port may be provided on the case accessing the second single pressure volume.

The invention of the present disclosure, in another aspect thereof, comprises a method including providing a substantially cylindrical case having a first, open end and a substantially cylindrical guide member inside thereof attached to a second end, the case and guide member being substantially coaxial, and inserting a piston that defines a hollow center between the case and guide member such that the guide member passes through the hollow center and the piston is movable along the guide member. The method includes attaching a fixed pressure barrier on and end of the guide member proximate the open end of the case such that the piston does not leave the case, attaching a first end of a hollow rod to the piston such that the hollow rod encircles the pressure barrier, and attaching a cap to a second end of the hollow rod, the cap being sized such that the cap and first piston are at least partially radially extensive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cutaway view of a hydraulic cylinder according to aspects of the present disclosure.

FIG. 2 is an end-on cutaway view of the hydraulic cylinder of FIG. 1.

FIG. 3 is a side view of the hydraulic cylinder of FIG. 1 shown in an extended position.

FIG. 4 is a side cutaway view corresponding to FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a side cutaway view of a hydraulic cylinder according to aspects of the present disclosure is shown. The hydraulic cylinder 100 has a case 102 having a closed end 103 and an opposite, open end 105. In the present embodiment the case 102 is generally cylindrical in shape. The case 102 and other components described herein may be constructed from steel or another material suitable for use in hydraulics. A attachment point 104 may be provided on the closed end 103 to allow the cylinder 100 to be attached to machinery or other implements. On the open end 105 is a second attachment point 106. In the present embodiment, the attachment points 104, 106 are simple loops but in other embodiments the attachment points 104, 106 may comprise clamps, knobs, threaded connections or other implements. The attachment points 104, 106 may also be considered hydraulic rams as explained in greater detail below.

In the present embodiment the attachment point 106 attaches threadingly to a hollow rod 114 and forms a hydraulic piston with the piston face 108 inside the rod 114. In some embodiments, the attachment point may be welded to the rod 114 or attached by other means. The piston face 108, in response to hydraulic pressure, will tend to urge the attachments 104 and 106 away from one another.

In the present embodiment a second piston 110 is provided inside the case 102. The second piston 110 is toroidal in shape in the present embodiment. Since FIG. 1 is a side cutaway view, the piston 110 may be seen at the top and bottom of the figure inside the case 102. The piston 110 provides a piston face 112 that will also tend to urge the ends 104 and 106 apart in response to hydraulic pressure.

A threaded cap or retainer 116 may thread into the case 102 in order to prevent the piston 110 from leaving the case 102 entirely. Various o-rings and seals are provided throughout the device 100 where needed to maintain proper hydraulic pressure. For example an o-ring seal is provided between the attachment point 106 and the hollow rod 114. The retainer 116 provides two o-ring seals 118, 120 for the case 102 and rod 114, respectively. In the present embodiment, an additional seal 122 is held by the retainer 116 and circumscribes the rod 114 and is held.

In the present embodiment, inside the case 102 and attached in a fixed relationship to the closed end 103 of the case 102 is a guide rod 124. In the present embodiment the guide rod is substantially cylindrical and hollow. The piston 110 may ride along the guide rod 124 as it moves within the case 102. An o-ring 134 seals the piston 110 against the case 102. A second o-ring 132 seals the piston 110 against the guide rod 124.

The guide rod 124 provides a tapered end 125 that is also threaded. In the present embodiment, a pressure barrier 126 is retained on the tapered end 125 of guide rod 124 by a threaded cap 128. In some embodiments the end 125 may stepped rather than tapered. The pressure barrier 126 is thus held in fixed relationship to the guide rod 124 and case 102. In some embodiments, the pressure barrier 126 threads directly to the guide rod 124. In order to effectively block high pressure from reaching a back side 113 of the piston 110 the pressure barrier may seal against the hollow rod 114. O-ring seals 128, 130 are provided for sealing the pressure barrier 126 against the hollow rod 114 and the guide rod 124, respectively.

One or more pressure equalization ports 123 may be defined in the guide rod 124 proximate the end 103 of the case 102. This allows a single high pressure volume 302 to be defined that includes: the variable volume bound by the piston 110, the case 102 and the guide rod 124; the volume bound by the interior of the guide rod 124; and the variable volume bound by the pressure barrier 126 and the piston 108. A high pressure hydraulic port 136 may be installed in the case 102 near the end 103. In response to hydraulic pressure supplies at the port 136, the volume 302 will expand forcing the attachment points 104, 106 apart. Due to the pistons 108, 110, having at least partial overlap in their radii, and the presence of the pressure barrier 126 on the guide rod 124, the expansive force of the attachment points 104, 106 will be increased. Depending upon the diameter of the guide rod 124 and the retainer 116, and the thickness of various components, the output of the cylinder 100 could approach twice the output of a traditional hydraulic cylinder at a given pressure.

The hollow rod 114 may have one or more pressure equalization ports 115 defined therein proximate the piston 110. This allows a single variable low pressure volume 304 to be defined by the two variable volumes including: the volume bound by the rod 114 and the guide rod 124 between the piston 110 and the pressure barrier 126; and the volume bound by the case 102 and rod 114 between the piston 110 and the retainer 116. In the present embodiment, the case 102 provides a low pressure hydraulic port 138 proximate the retainer 116.

In operation, any time a greater hydraulic pressure exists in the high pressure volume 302 than the low pressure volume 304, the ends 104 and 106 will be urged apart. If the low pressure volume 304 is pressurized to a greater degree than the high pressure volume 302, the ends 104 and 106 will be urged back together. (It is understood that under various operating conditions, it may be necessary for the pressure in the low pressure volume 304 to actually be higher than that of the high pressure volume 302.)

Referring now to FIG. 2 an end-on cutaway view of the hydraulic cylinder of FIG. 1 is shown (e.g., taken along line AA in FIG. 1). As previously described, the general shape of the case 102 may be that of a cylinder. Therefore when viewed as an end-on cutaway, the case 102 will appear circular. Here it can be seen how the piston face 108 is bound circumferentially by the hollow rod 114 (shown in ghost) behind piston 110. And the interior piston 110 is retained between the case 102 and the guide rod 124. From this view it can also be appreciated how, depending upon the thickness and diameter of various components, the amount of force available with a hydraulic cylinder of the present design can approach double that of a traditional design.

Referring now to FIG. 3, a side view of the hydraulic cylinder of FIG. 1 is shown. This view illustrates the cylinder 100 in an extended position. Here the hollow rod 114 is substantially fully extended and the first end 104 and second end 106 are further apart then shown in FIG. 1.

Referring now to FIG. 4, a side cutaway view corresponding to FIG. 3 is shown. As a result of a higher pressure in the volume 302 than in the volume 304, the piston 110, the piston 108, and the rod 114, have all extended away from the first end 103 of the case 102 forcing the ends 104, 106 apart. Because at least one pressure point 123 is defined in the guide member 124, high pressure can exist throughout the volume 302. Also, because the pressure barrier 126 prevents the high pressure from reaching both sides of the piston 110, at least a portion of the hydraulic forced input on port 136 is doubled within the cylinder 100 by the two pistons 110, 108.

Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims. 

1. A hydraulic device comprising; a case; and a substantially hollow rod slidably extending from the case, the rod having a ram on a first end thereof that caps the rod to form a first hydraulic piston, and the rod having a second hydraulic piston on a second end thereof, inside the case; wherein the first and second piston are at least partially radially coextensive, and a pressure barrier inhibits high pressure on the first piston inside the hollow rod from reaching a side of the second piston that faces the first piston.
 2. The hydraulic device of claim 1, further comprising a rod guide inside the case, and coaxial thereto, the second piston slidably interposing the case and the rod guide.
 3. The hydraulic device of claim 2, wherein the pressure barrier interposes the guide rod and the substantially hollow rod.
 4. The hydraulic device of claim 3, wherein a high-pressure, variable volume comprises a first volume inside the guide rod, a volume bound by the case and the second piston, and a volume between the first piston and the pressure barrier.
 5. The hydraulic device of claim 4, wherein a low-pressure, variable volume comprises an area bound by the case, the guide rod, the second piston, and the pressure barrier.
 6. The hydraulic device of claim 5, wherein the case and ram are urged apart by a relatively high pressure fluid inside the high pressure volume compared to the low pressure volume, and the case and ram are urged together by a relatively high pressure fluid inside the low pressure volume relative to the high pressure volume.
 7. The hydraulic device of claim 5, further comprising a high pressure port on the case entering the high pressure volume, and a low pressure port on the case entering the low pressure volume.
 8. The hydraulic device of claim 5, further comprising at least one pressure equalizing port defined in the rod guide.
 9. The hydraulic device of claim 5, further comprising at least one pressure equalizing port defined in the hollow rod.
 10. The hydraulic device of claim 3, wherein the case and rod guide have a substantially circular cross-section.
 11. The hydraulic device of claim 3, wherein the rod guide attaches inside the case on a first end thereof, and has a second tapered and threaded end that accepts the pressure barrier and retains the pressure barrier against the tapered end by an attached threaded cap.
 12. The hydraulic device of claim 11, further comprising a retainer on an open end of the case engaging the hollow rod and preventing the second cylinder from contacting the pressure barrier.
 13. A device comprising: a substantially cylindrical case having a first, open end and a substantially cylindrical guide member inside thereof attached to a second end, the case and guide member being substantially coaxial; a fixed pressure barrier on and end of the guide member proximate the open end of the case; a first piston defining a hollow center and located between the case and guide member, the piston being movable between the pressure barrier and the second end of the case; a hollow rod attached on a first end to the first piston, encircling the pressure barrier, and attaching on a second end to a second piston.
 14. The device of claim 13, wherein the guide member defines a pressure equalizing port proximate the second end of the case such that a first single pressure volume of variable total size is defined by 1) the variable volume bound between the first piston, the case, and the guide member, 2) the volume inside the guide member, and 3) the volume between the pressure barrier, the second piston, and the hollow rod.
 15. The device of claim 14, further comprising a hydraulic port on the case accessing the first single pressure volume.
 16. The device of claim 13, wherein the guide member has a tapered portion and a threaded end, the guide member retaining the pressure barrier between the tapered portion and the threaded end by an attached threaded cap.
 17. The device of claim 13, further comprising a retainer attached to the open end of the case and abutting the hollow rod on a side opposite the pressure barrier such that the hollow rod slides into the retainer, the retainer sealing the second end of the case to prevent the first piston from leaving the case
 18. The device of claim 13, wherein the hollow rod defines a pressure equalizing port proximate the first piston such that a second single pressure volume of variable total size is defined by 1) the variable volume bound inside the hollow rod, outside the guide member, and between the first piston and pressure barrier, and 2) the variable volume bound outside the hollow rod, inside the case, and between the first piston and retainer.
 19. The device of claim 18, further comprising a hydraulic port on the case accessing the second single pressure volume.
 20. A method comprising: providing a substantially cylindrical case having a first, open end and a substantially cylindrical guide member inside thereof attached to a second end, the case and guide member being substantially coaxial; inserting a piston that defines a hollow center between the case and guide member such that the guide member passes through the hollow center and the piston is movable along the guide member; attaching a fixed pressure barrier on and end of the guide member proximate the open end of the case such that the piston does not leave the case; attaching a first end of a hollow rod to the piston such that the hollow rod encircles the pressure barrier; attaching a cap to a second end of the hollow rod, the cap being sized such that the cap and first piston are at least partially radially extensive. 